1. Field of the Invention
The present invention relates to a lenticular lens sheet and a rear projection type screen used in a rear projection television or the like, and a method of manufacturing the lenticular lens sheet.
2. Description of the Prior Art
A rear projection type screen used in a rear projection television or the like generally has a composition in which two lens sheets are placed on top of one another. Specifically, a Fresnel lens sheet that narrows image light from a CRT (cathode ray tube) or image light that has passed through liquid crystals so as to make the image light be within a certain angular range is placed on the light source side, and a lenticular lens sheet that has a function of spreading out the image light that has passed through the Fresnel lens sheet into a suitable angular range is placed on the observer side.
A schematic perspective view of a rear projection type screen is shown in FIG. 7. As shown in FIG. 7, the rear projection type screen is basically composed of a lenticular lens sheet 1 and a Fresnel lens sheet 3. Lenticular lenses 11 are formed on the surface of the lenticular lens sheet 1 from which the image light enters (hereinafter referred to as the xe2x80x98light-entering surfacexe2x80x99). Of the surface of the lenticular lens sheet 1 from which the image light exits (hereinafter referred to as the xe2x80x98light-exiting surfacexe2x80x99), convergence parts 12 where light from the lenticular lenses 11 formed on the light-entering surface of the lenticular lens sheet 1 is converged are generally formed in convex lens shapes. The reason that the convergence parts 12 are formed in convex lens shapes is to improve the image light diffusion capability in the horizontal direction. Moreover, in the case of a lenticular lens sheet 1 used in combination with a 3-tube type CRT light source, it is necessary to form the convergence parts 12 in convex lens shapes in order to correct for color shift between the three colors. Non-convergence parts 13 where light from the lenticular lenses 11 formed on the light-entering surface of the lenticular lens sheet 1 does not converge (i.e. parts other than the convergence parts 12) are made to have a projecting shape with a summit portion thereof parallel to the lenticular lens sheet 1. An external light absorbing layer comprising a black coating or the like is provided on the summit portion of each projecting part by roll coating, screen printing, transfer printing or the like, thus forming external light absorbing parts 130. As a result, of external light entering the lenticular lens sheet 1, the amount of light that is reflected at the light-exiting surface of the lenticular lens sheet 1 and returns to the observer side is reduced, and hence the image contrast is improved.
A lenticular lens sheet 1 having a synthetic resin material such as an acrylic as a base material has minute undulations on the observer side, resulting in a feeling of the image being coarse and in there being no feeling of high quality, and hence to improve this situation, in recent years it has become common to provide a front faceplate 2 comprising an acrylic plate or the like on the observer side. Such a front faceplate 2 may also be referred to as a light-transmitting sheet, a protective shield or a contrast filter. However, providing a front faceplate 2 results in problems such as a reduction in productivity due to an increase in the number of components, and a reduction in contrast due to an increase in the number of surfaces that reflect external light. To resolve these problems, in Japanese Patent Application Laid-open No. H06-308615, Japanese Patent Application Laid-open No. H07-307912 and Japanese Patent Application Laid-open No. H08-22077, methods have been proposed in which the front faceplate is bonded to the lenticular lens sheet at external light absorbing parts of the lenticular lens sheet to form a single body.
Specifically, Japanese Patent Application Laid-open No. H06-308615 discloses a method in which black stripes, i.e. external light absorbing layers, are formed in advance on projecting parts, and then black adhesive layers are provided and bonding is carried out to form a single body. Moreover, Japanese Patent Application Laid-open No. H07-307912 discloses a method in which external light absorbing layers are formed, and are themselves used as adhesive layers. Furthermore, Japanese Patent Application Laid-open No. H08-22077 discloses a method in which external light absorbing layers are formed, and a film that is to be bonded on to form a single body is coated in advance with a transparent adhesive layer that becomes adhesive only under conditions such as application of heat and pressure or ultrasound, and then bonding is carried out, and a method in which fine carbon particles are dispersed into an adhesive to form a black adhesive, and this black adhesive is applied onto the external light absorbing layers to from adhesive layers.
However, in the case of the method disclosed in Japanese Patent Application Laid-open No. H06-308615, a two-liquid-type solvent-type adhesive is used, and hence there is a problem in that if the solvent is not completely evaporated, then blockage of light will occur due to the adhesive running out. This is because the speed of drying of the adhesive is greatly affected by the environment of the room, and hence is difficult to control. Moreover, another reason is that the adhesion width varies greatly with the extent of evaporation, and hence control is difficult. Furthermore, there is also a problem in that the lenticular lens sheet and the front faceplate may shift relative to one another between the two being bonded together and the adhesive hardening.
Moreover, in the case of the method disclosed in Japanese Patent Application Laid-open No. H07-307912, as well as the problem of blockage of light due to the adhesive running out, there is also a problem in that unevenness in the thickness of the external light absorbing layers occurs due to the summit portions of the projecting parts on the lenticular lens sheet not being completely flat, and hence a sufficient light blocking effect is not achieved in regions where an external light absorbing layer is too thin. This unevenness in the thickness may also be perceptible in terms of the external appearance, in which case there will be a reduction in the image quality.
Furthermore, in the case of the method disclosed in Japanese Patent Application Laid-open No. H08-22077, the front faceplate must be thick, and hence a method such as thermocompression bonding cannot be adopted. Moreover, in the case of a transparent adhesive layer, there is a problem in that external light from the front faceplate side that is incident upon the interface between the edge of the transparent adhesive layer and the air is reflected at this interface, resulting in an increase in reflection of external light and hence a worsening of the contrast.
As described above, there are thus problems with the conventional art such as blockage of light caused by the adhesive used to bond the lenticular lens sheet and the front faceplate together.
In view of the foregoing, it is an object of the present invention to provide a lenticular lens sheet and a rear projection type screen, for which adverse effects caused by blockage of light are prevented.
It is another object of the present invention to provide a lenticular lens sheet manufacturing method, for which adverse effects caused by blockage of light are prevented.
According to one aspect of the present invention, for achieving the above-mentioned object, there is provided a lenticular lens sheet that is bonded to a front faceplate and used in a rear projection type screen, the lenticular lens sheet having a plurality of lenticular lenses arranged on one surface of a light-transmitting substrate, and projecting non-convergence parts arranged on the other surface of the light-transmitting substrate in positions different to positions of convergence of light from the lenticular lenses, wherein an external light absorbing layer that absorbs external light is provided on a summit portion of each of the projecting non-convergence parts, and wherein the lenticular lens sheet and the front faceplate are bonded together at the summit portions of the projecting non-convergence parts using an adhesive, and the width of adhesive layers formed through curing of the adhesive is less than the width of the external light absorbing layers.
Consequently, the adverse effects caused by blockage of light are prevented.
According to another aspect of the present invention, there is provided a method of manufacturing a front-faceplate-equipped lenticular lens sheet that is used in a rear projection type screen, has a front faceplate bonded thereto, and has a plurality of lenticular lenses arranged on one surface of a light-transmitting substrate, and projecting non-convergence parts arranged on the other surface of the light-transmitting substrate in positions different to positions of convergence of light from the lenticular lenses, the method comprising the steps of providing an external light absorbing layer that absorbs external light on a summit portion of each of the projecting non-convergence parts and bonding the lenticular lens sheet and the front faceplate together using an adhesive at the summit portions of the projecting non-convergence parts, and then curing the adhesive, such that the width of adhesive layers thus formed is less than the width of the external light absorbing layers.
Consequently, the adverse effects caused by blockage of light are prevented.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for purpose of illustration only and are not intended as a definition of the limits of the invention.